Speed governing system for a fuel injected internal combustion engine, especially a diesel engine

ABSTRACT

To provide for smooth operation of a fuel injected engine, typically a diesel engine, if the diesel engine is controlled to reduce speed and towards idling thereof, it is first determined if the actual speed (n) of the engine drops below a certain speed threshold (NS), the commanded speed (N), upon such sensed occurrence is evaluated and the time rate (1/K) of an exponential function of commanded rate of drop in engine speed is changed as a function of the decrease (dn/dt) of the actual speed of the engine. Engine temperature can be used to modify the speed threshold, and the rate of change can, additionally, be evaluated with respect to a predetermined rate of change of speed of the engine. A difference between commanded and actual speed, applied to a proportional-integral controller can be used with an offset which offset becomes effective only upon rise of engine speed after a prior drop. The system can be made sensitive to engine temperature and prevents bucking of the engine, particularly when cold, at which time a drop from a higher engine speed level to a lower speed level may occur at an excessive rate without touch control.

This application is a continuation, of application Ser. No. 741,182,filed June 4, 1985 now abandoned.

Reference to related patent assigned to the assignee of presentapplication, the disclosure of which is hereby incorporated byreference.

U.S. Pat. No. 4,425,888, Engel, et al.

The present invention relates to a speed control system and moreparticularly to a speed control or speed governing system for a fuelinjected internal combustion engine, especially a diesel engine, inwhich an idle speed fuel controller which has proportional-integratingcharacteristic, is used.

BACKGROUND

The referenced U.S. Pat. No. 4,425,888, Engel, et al., assigned to theasignee of the present application describes a speed control orgoverning system for an automotive-type internal combustion engine,especially a self-ignited internal combustion engine, that is, forexample of the diesel engine type. In accordance with the disclosure ofthe reference, the command value of speed is raised by aproportional-integrating acting controller when the actual speed hasreached a predetermined relationship with respect to the command speed.In such a speed control system, commanded speed is changed when thedifference between actual speed and commanded speed reaches apredetermined level or value. The difference between actual speed andcommanded speed is maintained constant.

As the speed drops, particularly when the speed drops below a lowerthreshold level, a different control function becomes effective. Thedrop in commanded speed is then matched, at least roughly, to the actualspeed drop, as determined by operating characteristics of the enginewhen it has normal operating temperature.

If the engine is cold, the actual speed drop may be more rapid than thespeed drop when the engine is warm. Consequently, it is possible thatthe controller will not follow rapidly enough the actual changes inspeed of the engine and a predetermined minimum idle speed may actuallybe passed, by the engine when it is still cold and the engine willstall. The control system, as described, while functioning well with anengine which is warm may not prevent stalling of the engine due to theexcessively rapid speed drop when the engine is still cold.

THE INVENTION

A proportional integrating controller receives as an input thedifference between an instantaneous commanded engine speed, for example,derived from a table, or engine characteristics, and the actualinstantaneous engine speed; data representing commanded decrease inengine speed, in accordance with an exponential (e) function areprovided. In accordance with a feature of the invention, the temporalcourse of drop of engine speed below a predetermined speed threshold NSis sensed and the level of the command speed is evaluated. If a drop inspeed below the predetermined speed threshold NS, which is above idlingspeed, has been determined or sensed, the time rate of the exponentialfunction of speed drop is then controlled to gradually, or more slowlyapproach idling speed of the engine. The rate of decrease of enginespeed is thereby more accurately controlled and can take care of changesin engine operating characteristics, based on temperature of the engine.

In general, the invention relates to control of the speed drop towardsidle speed of an internal combustion engine (ICE), typically a dieselengine. The temporal course of commanded speed drop, as well as drop ofactual speed, will occur in accordance with a drop of an exponentialfunction. The time constant of the exponential function is formed orcontrolled in dependence on operating parameters of the ICE.

The invention is not limited to a specific type of ICE, and several, orall operating parameters of the ICE can be used to influence, ordetermine the exponential function.

In accordance with a feature of the invention, the system carrying outthe function can be derived to operate, as desired, in analog mode, or,with well known engineering changes, in digital mode.

The speed control or governing system in accordance with the inventionhas the advantage to provide for trouble free control of speedregardless of then pertaining engine operating characteristics, forexample, engine temperature. Different types of engines will reactdifferently to different temperature conditions of the engine. Thesystem is adaptable to various types of engines and ensures, for alltypes of engines suitable operating speed under idling conditions,regardless of the then pertaining temperature or other operatingconditions of the engine.

The course of drop of actual engine speed may be more rapid when theengine is cold than when it is warm. The control system becomes onlyeffective when the actual engine speed drops below the predeterminedthreshold NS. In accordance with a feature of the invention, the rate ofchange of speed, that is, the rapidity of the drop itself is controllednot to fall below a minimum value. A slower drop of speed from, forexample, an operating speed to idling speed thus can be commanded. Thetime constant of the exponential function of the commanded speed changewill depend on the respectively measured speed drop of actual speed, andcan be controlled or made proportional to a fixed factor which is set.The set point can be adjustable. The specific factor can be selected, orset with respect to the operating characteristics of a specific type ofengine, and the speed relationships, or speed changes of the particulartype of engine with respect to operating parameters, such as temperaturefor example. It is thus easily possible to construct a basic system andthen match the particular system to a particular engine type, by merelychanging the respective factor, which will involve, from a circuit pointof view, for example, changing only the resistance value, or aresistance/capacity value in a circuit structure, which can be readilyaccomplished on integrated circuits (ICs) by a laser, or, otherwise bysetting a potentiometer.

When the desired, that is, commanded idling speed is reached, controlwill become effective only when a predetermined speed offset, or speeddifference is exceeded, and, thereafter, the actual speed again drops.Minor changes in speed which do not interfere with smooth running of theengine, even under idling conditions can be compensated for so that thespeed control will not become effective due to minor oscillations orhunting and thus prevent uneven engine operation.

DRAWINGS

FIG. 1 is a speed-time diagram illustrating the actual speed-timerelationship and commanded speed-time relationship as the actual speeddrops, illustrated with respect to a cold diesel ICE;

FIG. 2 illustrates the same characteristics as FIG. 1, but with theengine warm, that is, at normal operating temperature;

FIG. 3 is a diagram similar to FIG. 1 illustrating the characteristicsof the engine, that is, actual speed and commanded speed with afollowing course of increase in commanded speed; and

FIG. 4 is a general schematic block circuit diagram illustrating asystem suitable for carrying out the control functions in accordancewith the invention.

DETAILED DESCRIPTION

In the diagram of FIGS. 1 to 3, NS is a predetermined speed threshold;NL is an idle speed threshold or limit, which is a predetermined value;N the commanded speed and n the actual engine speed. The abscissa itrepresents a time axis.

The speed curve for actual speed, n, drops rapidly, as shown in FIG. 1,when, for example, the driver of the vehicle in which a diesel engine isinstalled lifts the foot off the accelerator pedal. The illustration ofFIG. 1 shows engine speed when the engine is cold. As soon as the speedthreshold level NS--determined, for example, by experimental or enginecharacteristics, has been passed, the control system becomes effectiveand determines the rate of change of actual engine speed, dn/dt. Therate of change of speed, that is, the change of speed per unit time isdetermined. When the rate of change of speed drops below a predeterminedfixed minimum rate n_(dmin) then, at time t=0, the commanded speed israised so that the commanded speed N will drop with a shallowexponential function, which has a comparatively long time, t_(off). Thecourse or function of the commanded speed N will follow, without change,in accordance with this predetermined exponential, or e-function, thetime constant of which is determined, essentially, by the a desired rateof drop in engine speed, which has previously been measured, that is, inaccordance with a previously measured relationship dn/dt of the specificengine. Engine operating parameters, for example temperature can be usedto influence or control the time constant. Change in the course of thecommanded speed N will only become effective when the actual speed againbegins to rise. The operation of the control system as speed rises willbe described below in connection with FIG. 3.

After the engine has warmed, the characteristics of the rate of changeof engine speed will be somewhat different. FIG. 2 illustrates thecharacteristics of actual speed n with the warm engine and it can beseen that the rate of actual drop in speed dn/dt is less than that inFIG. 1; the commanded speed N thus will have a shorter off time t_(off),than in FIG. 1. These characteristics shown in FIG. 2 are a good exampleof the change in speed when the engine has reached normal operatingtemperature.

Both in FIGS. 1 and 2, the difference between predetermined idle speedfixed threshold NL and the threshold NS at which time NS the systembecomes effective is the same. It may be desirable, however, to slightlyraise the speed level of the idle speed threshold NL if the engine isstill cold. The idle speed threshold NL with a cold engine, can be soincreased that the engine will operate smoothly, and without bucking.Since, in a warm engine, increased idle speed is not necessary fornormal smooth non-bucking engine operation, the idle speed can be dropedto a lower level. This results in a decrease in engine noise, lessexhaust gases, less stress on materials, and less use of fuel. In atypical automotive-type diesel engine, the predetermined idle speed NLat a cold ICE can be set for 1000 rpm, whereas, when the engine hasreached normal operating temperature, the idle speed may be set for 600rpm.

The command value for the idle speed NL can be changed in accordancewith engine temperature simply by including a temperature signal derivedfrom a temperature sensor in the control function; such a signal can beapplied to a computer or otherwise standard engine control system whichthen computes the required engine idling speed based on enginetemperature, for example, by addressing a previously determined table,for example, stored in a read-only memory (ROM) and then, based ontemperature, applies the respective corresponding value to the controlsystem. The speed threshold NS at which the system becomes effectiveremains at the predetermined value (see FIGS. 1, 2).

FIG. 3 illustrates the two characteristics for actual speed n andcommanded speed N, if, after the ICE reached idling speed, i.e., at timet₁ an increase in speed is controlled, for example, by the operator.This increase in speed may be caused by depression of the acceleratorpedal in an automotive engine. The commanded speed N in the controllerfollows the actual speed n but only when the actual speed n has exceed aspeed offset value NO. The following conditions, thus, must be met:

    n↑(rising) and n-N>NO

The following of the commande speed N thus will occur only--with risingactual speed--when the difference between the actual speed n and thecommanded speed N is greater than the previously determined, forexample, predetermined speed difference or speed offset NO.

Upon subsequent drop of actual n the commanded speed N will again dropin accordance with an exponential function, the time constant of whichcorresponds to the time constant which was previously determined at theprior drop below the threshold level NS. Thus, the commanded speed Nwill be governed by the following relationship:

    N=NL+(NS-NL)e(-t/K)

wherein

    K=dn/dt·KV+KO

In the foregoing, N again is commanded speed, NL the idle speedthreshold, NS the predetermined response speed threshold, dn/dt the rateof actual speed drop at the time the threshold NS is passed; t is theengine operating temperature; KV is the amplification factor of thecontrol amplifier of controller R, and KO is the offset constant, whichdetermines the speed offset NO (FIG. 3).

A system to carry out the control method in accordance with the presentinvention is shown in FIG. 4, to which reference will be made; FIG. 4illustrates only the necessary elements, in block circuit configuration,to carry out the method of control. The diagram is schematic andrepresents a suitable circuit in analog form; it is, equally possible,to carryout all of the control functions described in analog form withreference to FIG. 4 by a suitably programmed digital computer orcontroller, as well known in digital control technology. The variousfunctions can be obtained or realized by software. For example,temperature sensing can be carried out either by a temperature sensorproviding an analog output signal, or by interrogating output levelsderived from an engine temperature sensor and comparing the level withtables storing, at respective addresses, signals representative oftemperature levels which, then, can command further control functions,based on the level derived from the sensor.

Essentially, this control system of FIG. 4 has a command value generatorGS, a proportional-integrating controller R, and an ICE, which receivesthe output signals from the proportional-integral (PI) controller R. ThePI controller R, at its input, received the difference between commandedspeed N and actual speed n of the ICE.

The actual speed n of the ICE is applied to a function generator 1which, in dependence on the rate of change of speed dn/dt, and independence on the desired or commanded idle speed threshold NLdetermines the course or rate of change for the commanded drop in speed,that is, the commanded speed curve N. The function generator 1 onlybecomes effective when the actual speed n passes the predetermined speedthreshold level NS. The rate of change, that is, the rate of speed dropmust exceed a predetermined minimum speed change n_(dmin).

A first transfer switch 2 is coupled to the output of the functiongenerator 1 which, if the foregoing conditions all pertain, will changeover from the position shown into the broken line position, so that,then, the output of the function generator 1 will be coupled to oneinput terminal of a difference forming or subtraction circuit S.

For the time that the actual speed n is above the threshold NS, transferswitch 2 is as shown in the full line position; likewise, a secondtransfer switch 3 will be in the full line position as shown. Thetransfer switch 3 is changed over based on control from a controlelement 4 into broken line position which determines if the condition isfulfilled:

    n↑ (n-N)>NO

The condition for changeover of the first transfer switch 2 from fullline to broken line position is determined by the logic element 5 whichdetermines the following condition:

    n↓ n<NS

Temperature of the ICE is sensed by a temperature sensor TS, whichprovides a temperature output signal, schematically shown at terminal Tto control, for example, the level of the thresholds NL and/or NS. Sincethe logic conjunction as determined by the logic circuits 4,5 may dependon the then pertaining temperature, and since temperature may affect thelevels NS, the temperature signal, or a representation thereof, forexample in digital form, is preferably applied to the logic circuits 4,5as well. The actual construction of the logic circuits is well known andcan be done in accordance with any suitable engineering practice, forexample, in digital or analog form. The temperature signal at terminal Tcan also control the time constant of the exponential functioncontrolling engine speed decrease.

Various changes and modifications may be made within the scope of theinventive concept.

What is claimed:
 1. A method of controlling the operation of a fuelinjected internal combustion engine (ICE), especially a diesel engine,upon commanding decrease of engine speed in a direction towards apredetermined idling speed (NL),utilizing an idle speed controller (R)which has proportional-integrating characteristics, said methodcomprising establishing a predetermined speed threshold (NS) which isabove the predetermined idling speed (NL); supplying an input signal tothe controller (R) representative of the actual instantaneous speed ofthe engine (n); supplying an input signal to the controller (R)representative of a commanded instantaneous engine speed (N) of theengine;determining when the actual speed (n) of the engine drops belowsaid predetermined speed threshold (NS), and generating a controlsignal; and controlling the commanded rate of change of speed of theengine upon sensing that the actual speed (n) of the engine has droppedbelow said predetermined speed threshold (NS) towards said predeterminedand lesser idling speed (NL) of the engine in accordance with anexponential function (e), wherein the exponential function determiningthe rate of change of speed is defined as follows:

    N=NL+(NS-NL)e.sup.(-t/K)

wherein

    K=dn/dt·KV+KO

and wherein dn/dt is time rate of change of actual engine speed andwherein KV is a constant KO is a constant t represents time NLrepresents the predetermined idle speed; NS the predetermined speedthreshold; and dn/dt the actual rate of drop in engine speed.
 2. Themethod of claim 1 including the step ofdetermining, if the actual rateof decrease (dn/dt) of engine speed falls below a predetermined fixedminimum rate (n_(d) min); and wherein said step of controlling thecommanded rate of change (d_(n/dt)) of the actual engine speed towardsthe predetermined idling speed is carried out only if the rate of changeof actual engine speed (dn/dt) exceeds said predetermined fixed minimumrate.
 3. The method of claim 1 including the step of setting theconstant KV as a determinable adjustable amplification factor of anamplifier.
 4. The method of claim 1 including the step of sensing thetemperature of the engine and deriving a temperature-representativesignal (T);and including the step of raising said predetermined speedthreshold (NS) if the sensed temperature of the engine is below a normaldesign operating temperature thereof.
 5. The method of claim 1 includingthe step of sensing the temperature of the engine and deriving atemperature-representative signal (T);and raising said predeterminedidling speed (NL) if the sensed temperature of the engine is below anormal design operating temperature thereof.
 6. The method of claim 1including the step of sensing the temperature of the engine and derivinga temperature-representative signal (T);and raising both saidpredetermined speed threshold (NS) as well as the predetermined idlingspeed (NL) if the sensed temperature of the engine is below a normaldesign operating temperature thereof.
 7. The method of claim 1 includingthe step of measuring the actual rate of change (dn/dt) of decrease inengine speed;and utilizing the thus measured value in the relationshipor factor K of claim
 1. 8. The method of claim 1 including the stepsofcommanding an idle speed level at said predetermined idling speed(NL); determining when the actual speed (n) of the engine has reached,at least approximately, the so commanded idling speed level (NL); andupon supply of fuel to the engine to increase engine speed, controllingthe controller (R) by the difference between commanded engine speed andactual instantaneous engine speed in such a manner that the commandedengine speed (N) follows the actual engine speed (n) upon increase inactual engine speed only with a difference, or offset (NO) during acontinued condition in which the actual engine speed (n) is below saidpredetermined speed threshold (NS).
 9. The method of claim 8includingthe step of further controlling the controller (R) by applyingthe difference thereto upon subsequent dropping of actual engine speed(n), and controlling said drop of engine speed in accordance with saidexponential function set forth in claim
 1. 10. The method of claim 1wherein the constant KV is a controllable constant;including the stepsof determining an operating parameter of the engine; and controlling thetime constant (e) of the exponential function in dependence on the sodetermined operating parameter of the engine by controlling said timeconstant as a function of said operating parameter.
 11. The method ofclaim 10 wherein said operating parameter of the engine which controlsthe time constant (e) of the exponential function comprises temperatureof the engine.
 12. The method of claim 1 wherein the controller (R)includes an amplifier of controllable amplification ratio;and whereinsaid constant KV is the amplification factor of the control amplifier.13. The method of claim 8 wherein the constant KO in the relationship ofclaim 1 is representative of engine speed difference or offset (NO) fromcommanded speed.